1. Field of the Invention
The invention pertains to a method and to an apparatus for controlling the brake system of a vehicle according to introductory clauses of the independent claims.
2. Description of the Prior Art
An automatic, electrically controlled brake system for a vehicle in which, by way of an appropriate interface, the brake system of a trailer or semitrailer can additionally be controlled by means of an open-loop or closed-loop control circuit is known from SAE Paper 92 24 89, "Brake by Wire for Commercial Vehicles". In combination vehicles of this type, the forces which occur between the component vehicles when the train is braked, especially the force in the longitudinal direction, is especially important, because they can have an effect on both driving comfort and driving safety. The goal of the open-loop or closed-loop control of the brake systems of a combination vehicle of this type is to minimize these forces. It has been found that the different brake hystereses of the component vehicles, that is, the fact that the brakes of the component vehicles require different lengths of time for their application and also for their release, make a considerable contribution to the occurrence of these longitudinal forces. Therefore, ways have been sought in the past to determine the points at which the brakes of the component vehicles are applied and/or released.
For example, DE 41 12 845 A1 describes a compressed-air brake system, in which, when the brakes are actuated, the change in pressure over time is evaluated to determine the application point and the associated actuating variable of the individual wheel brakes. In addition, a procedure is known from not previously published German Patent Application No. 195 218 72.8 of Jun. 16, 1995, according to which the application and/or release of the trailer or semitrailer brakes can be determined by an identification procedure during the buildup and reduction of the braking force, in that inflection points in the deceleration curve of the overall vehicle are detected. By means of such measures, the actuating variables to be specified for the application and/or release of the wheel brakes of the component vehicles of a vehicle train can be derived.
Taking these values into consideration in the control of the brake systems makes a significant contribution to the improvement of the braking behavior. In spite of this improvement, however, transient defects in the coordination of the brakes of the component vehicles can occur during the buildup or reduction of the braking force as a result of the dead times which are caused by, for example, the length of the brake lines leading to the trailer's brakes. One of the signs of this situation is, for example, when the trailer bumps into the rear of the tractor; this occurs as a result of a delay in the buildup of the braking forces in the trailer's brakes.